Six global powers will launch a diplomatic drive after the US elections aimed at defusing the Iranian nuclear crisis in the next few months and avoiding the eruption of a new Middle East conflict next year.

A "reformulated" proposal will offer limited relief from existing sanctions and other incentives for Iran to limit the level of enrichment of its uranium stockpile. An attempt will be made to sequence the steps required to reach a deal to overcome the mutual distrust that helped sink previous rounds of negotiations, where each side appeared to wait for the other to make the first major concession.

"We recognise that the Iranians need something more with which they can sell a deal at home, and we will expect real change on the other side. It is about getting the sequencing right. That is what this next round will be about," a European official said.

"If Iran is prepared to do enough, sanctions will be on the table," another western diplomat said. "It shouldn't expect [the six-power group] to blink first – but if it's ready to take genuine steps we're ready to respond. This could include sanctions relief – but only for the right moves by Iran. Sanctions are biting in Tehran and we're not going to lift them without making solid progress on our concerns."

If the step-by-step approach fails there could be an attempt to "go big" with an ambitious, comprehensive settlement that would allow Iran to continue producing uranium at low levels (under 5%) of enrichment but under stricter international monitoring and controls.

"Currently we are stalled because Iran is asking too much and offering nothing in return. One way forward might be for Iran to offer much more and make an accordingly bigger demand at the same time," the western diplomat said. Officials involved in the nuclear talks believe there is a window of opportunity for diplomacy between the US elections on 6 November and next spring, with a resumption of high level talks between the group of six powers (the US, UK, France, Germany, Russia and China) with the Iranian chief negotiator, Saeed Jalili, in late November or December.

"Elections obviously mean there's a great deal of uncertainty, but there will be more clarity after November and clearly that's an opportunity," one western diplomat said. Britain will be represented at the talks by Mark Sedwill, formerly the UK's special envoy to Afghanistan and Pakistan, who has been named the new political director of the Foreign Office.

Much will hinge on the outcome of next month's presidential elections. The plan assumes that either Barack Obama wins a second term, or that Mitt Romney wins but allows the diplomatic initiative to go forward unchanged. If a victorious Romney insists on a full policy review after taking office, the nuclear diplomacy could be derailed for months.

Diplomats who took part in the last abortive round of high-level talks in Moscow in June said Jalili made it clear that Iran did not think it was worth negotiating seriously until it was known who the US president would be next year. Western officials also believe that the devastating effect of new energy and banking sanctions made Tehran readier to engage in substantive bargaining.

"Their economy is falling about their ears, so we think they are rather more willing to engage now than in Moscow," a European diplomat said.

In an effort to ratchet up the pressure, European foreign ministers are due to meet in Luxembourg on Monday to agree a further tightening of sanctions, imposing bans on more Iranian banks and closing loopholes in shipping restrictions imposed in the summer.

The diplomatic opening is expected to close again in the spring, as the Iranian leadership is likely to be distracted by the campaign for the country's own presidential elections in June.

Iranian politics is just one of the clocks ticking on the new diplomatic initiative. The Israeli prime minister, Binyamin Netanyahu, warned at the UN general assembly last month that the Iranian nuclear programme would reach Israel's "red line" by "next spring, at most by next summer", implying that Israel might then take military action in a bid to destroy Iranian nuclear sites and set back the programme.

That red line, which Netanyahu illustrated at the UN with a marker pen on a ~picture of a bomb, is defined by Iranian progress in making 20%-enriched uranium, which would be much easier than 5% uranium to turn into weapons-grade fissile material should Iran's supreme leader, Ayatollah Ali Khamenei, take the strategic decision to "break out" from Iran's observance of the Nuclear Non-Proliferation Treaty, to try to make a weapon. Tehran insists it has no such intention.

A report published this week by the Institute for Science and International Security in Washington said that if Iran tried to break out now, it would take its centrifuge plants between two and four months to make enough weapons-grade uranium for a single warhead. As Iran builds up its 20% uranium stockpile, the ISIS report said a breakout could take less than one month, giving Israel and the west much less time to respond and increasing the chance of a pre-emptive strike.

However, it would take several times longer to build even a small nuclear arsenal, and Iran itself has set back that timetable by converting about a third of its 20% stockpile into oxide fuel, which would be harder to turn into weapons-grade material.

The 20%-enriched uranium stockpile would be at the heart of the new diplomatic effort. In Moscow meeting in June, the six-nation group of negotiators proposed that Iran should stop producing it, ship its stockpile of almost 200kg out of the country and shut its underground centrifuge plant in Fordow where much of it is made.

In return, Iran would be given fuel plates to use in its Tehran medical research reactor (for which it says it requires the 20% uranium), help with nuclear safety, and spare parts for civilian airliners which are currently under sanctions.

In return, Jalili presented an uncompromising document which called for all sanctions to be lifted with no let-up in Iranian enrichment. "Their ideas are a non-starter from an American perspective," a senior US administration official said.

However, several US analysts criticised the west's negotiating stance at Moscow, arguing Iran had no incentive to offer concessions on enrichment when there was no prospect of relief from punishing sanctions.

"The offer of airplane parts was an insult," said George Perkovich, a nuclear expert at the Carnegie Endowment for International Peace. He said that for a deal to stick, Khamenei had to retain the capacity to restart uranium enrichment at the underground site at Fordow as a form of insurance in case the west broke its side of the bargain. "The supreme leader is absolutely convinced that the US will renege, so what is his leverage? It has to be Fordow. He has to be sure he can go back to Fordow and crank it up."

Western officials said that at a meeting in Istanbul in July, experts from Iran and the six-nation group discussed compromise options for stopping production at Fordow in a way that would also allow it to be restarted. They insist that it was privately made clear to Jalili in Moscow that significant sanctions relief would follow if Iran showed a readiness to compromise on 20% enrichment, but some now acknowledge that a more concrete offer needs to be made for Jalili to be able to "sell" the deal to Iran's supreme leader.

Jim Walsh, an expert on the Iran nuclear programme at the Massachusetts Institute of Technology, said: "This period between the US elections and the Iranian elections is the last best chance to turn this thing around… I think the Iranians are ready and the Americans are ready. It's a question of the whether the optics and politics can be made to line up this time."